Strand tension control apparatus



Dec. 10, 1963 R. c. STEEN 3,113,746

STRAND TENSION CONTROL APPARATUS Filed D80. 29, 1961 2 Sheets-Sheet 1 FIG. I

INVENTOR.

R. 6. .5 TE E N Dec. 10, 1963 R. c. STEEN s'rmmn TENSION coumor. APPARATUS 2 Sheets-Sheet 2 Filed Dec. 29. 1961 CO/LS THYRATRON C/RCU/T RECTIFIER Fla. 3

AMPLIFIER OSCILLATOR INVENTQR. R. C. STEE/V United States Patent 3,113,746 STRAND TENSTUN CQNTRGL APPARATUS Richard C. Steen, Flemington, N..l., assignor to Western Electric (Iornpany Incorporated, New York, N.Y., a corporation of New York Filed Dec. 29, 1961, Ser. No. 163,285 3 Claims. (til. 242155) This invention relates to strand tension control apparatus and more particularly to apparatus for controlling the tensioning of a rapidly moving continuous filamentary strand.

In many manufacturing operations it often is necessar to control the tension of a moving strand. For instance, in the manufacture of electrical coils from fine, delicate wires, it is necessary that the wire tension be maintained at a low value during winding to avoid breaking of the fragile wire and to minimize the destructive eifect of tension on the wire insulation, typically a thin film of enamel. In addition to keeping the tension low, it is of substantial importance that the tension be maintained constant in order to produce an even distribution of the wire on a bobbin or spool.

Many strand-advancing systems are known to the art, but most control systems therefor are complicated and introduce so much tension themselves as to render them inadequate in applications requiring a low tension. Further, prior art control systems are generally not sufficiently sensitive or responsive to give the fine control that is so advantageous in many commercial applications.

Accordingly, it is an object of this invention to provide new and improved strand tension control ap aratus.

Another object of the invention is to provide a sensitive and responsive apparatus for controlling the tension of a rapidly moving filamentary strand, which does not itself impose a large tension on the strand.

Apparatus illustrating certain features of the invention may include a rotatable member, at least a portion of which is electrically conductive, mounted between a strand supply and a strand receiver, typically a spool on a rotating shaft. Pole pieces of an electromagnet are positioned adjacent to portions of the member. The motion of the member, caused by advancement of the strand, through the magnetic field generates rotation-retarding eddy-current in the member, thereby tensioning the strand. A feedback path from a tension sensor controls the energy supplied to the electromagnet. The tension sensor preferably comprises strain gauges mounted on a cantilevered beam having a pulley at its free end over which the strand passes.

A more complete understanding of the invention may be obtained from the following detailed description of an apparatus forming a specific embodiment thereof when read in conjunction with the drawings, in which:

FIG. 1 is a side view, in perspective, of the tension control apparatus forming a specific embodiment of the invention;

FIG. 2 is a top perspective view of another portion of the apparatus shown in FIG. 1, with parts broken away, and illustrating the tension sensor; and

FIG. 3 is a schematic diagram of an electrical circuit forming a part of the apparatus shown in FIGS. 1 and 2.

Referring now in detail to the drawings, wherein like numerals designate the same elements throughout the several views, there is shown in FIGS. 1, 2, and 3 strand tension control apparatus for controlling tension on a strand 11 advancing from a supply reel 12 to a take-up spool 13. The strand llll may be, for instance, a wire with an enamel insulation to be wound into a coil on the spool 13. The spool 13 is mounted on a shaft 14 of a motor 15 which supplies the power for both winding the strand on the spool 13 and dereeling the strand from the reel 12.

Patented Dec. 10, 15263 The main elements of the strand tension control apparatus are a guide assembly generally designated by the numeral 16, a tensioning assembly generally designated by the numeral 17, and a tension sensing assembly generally designated by the numeral 18.

In order to obtain high sensitivity and responsiveness in the system, it is of great importance that the inertia be kept low. Accordingly, the reel 12 is arranged for over-the-end dereeling, i.e., the strand is pulled from one end. This eliminates the large inertia that would be induced by a revolving supply reel. It is thus an important feature of the invention that the tensioning assembly 17 is separate from the supply reel 12.

The guide assembly 16 is mounted on a bracket 19, which is supported by a stand 20, and comprises a first guide cone 21, felt padding 22, a second guide cone 23, back tensioning rollers 24, and a guide pulley 25 mounted on a guide arm 26. The reel 12 is arranged for overtheend dereeling by placing the spool on one end thereof. As the strand i1 is pulled oil of the reel 12, it is gathered by the first guide cone 21 and directed through the felt padding 22 for cleaning foreign matter from the strand ill. The second guide cone 23 then directs the strand 11 through the back tensioning rollers 24. The back tensioning rollers are advantageously spring loaded and adjustable, whereby suificient tension, for example 3 or 4 grams, may be placed on the strand 11 to insure its firm contact with the other elements of the control apparatus. The guide pulley 2-5, which is advantageously constructed of nylon or other lightweight material to keep its inertia low, guides the strand fill into the tensioning assembly 17.

The tensioning assembly 117 includes an aluminum disk 29 axially mounted on a support arm 39 by means of suitable anti-friction bearings. The support arm 39 is attached to a cross member 31. A plate 32 is also supported on the cross member 31, and attached to the plate 32 are the tension sensing assembly 13 and the core of an electromagnet 33 having a pair of pole pieces 2%. Two electrical coils 27 are mounted on the core 33.

The strand ill is looped approximately once within a groove in the periphery of the aluminum disk 29. The disk 29 is positioned such that a portion of its periphery always lies within the air gap of pole pieces 28.

The support arm 3%) is pivotally attached to the cross member 31 by screws 5d and 51. Screws 5% and 51 have conical ends which fit within corresponding conical depressions in the support arm 39. The support arm 30 is removably maintained against pivoting around the axis of screws 56 and 51 by permanent magnets 52, which are fixed to the support arm 36 and grip the cross member 31. In this manner the disk 29 may be centered within the air gap of pole pieces 28. Further, the assembly of the disk 2h and the support arm 36 may be pivoted downward by applying hand pressure to permit the strand 11 to be easily looped around the periphery of the disk 29..

When the strand is advanced by the motor 15, the frictional engagement of the strand 1'1 with the periphery of the disk 29 will rotate the disk 29 through the gap between the pole pieces 28 thereby cutting the magnetic fiuX established by current through coils 27. As the disk 29 is made of conductive material, eddy currents will be inducted therein which will in turn interact with the magnetic flux to produce a force retarding the rotation of the disk 29. This force is proportional to the magnitude of the current through coils 27 and the rate of advancement of the strand 1].. Thus the strand 11 is tensioned between the spool 13 and the disk 29. In order to keep the inertia of disk 29 as low as possible it is advantageously comprised of a hub 53, a rim 5%, and spokes 55. The width of the rim 54 of the disk 29 in a radial direction should preferably be approximately equal to the depth of the air gap between pole pieces 23.

in order to control the tension of the strand 11, the current in coils 27 is determined by a feedback path which includes the tension sensing assembly 18 and the electrical network of FIG. 3.

The tension sensing assembly includes a flexible beam 3 5- cantilevered on a support block 35 mounted on the plate 32. A lightweight freewheeling pulley 3-6 is attached to the free end of the beam 34. A portion of the strand between the spool 13 and the disk 29 is passed around the upper half of the pulley 36. Thus the beam 34 is deflected to an extent proportional to the tension on the strand 11. Four resistance type strain gauges, which may advantageously be of the type manufactured by the Baldwin Lima Company under No. FAB25-35, are attached to the beam 34 in order to measure its deflection. Strain gauges 3'7 and 33 are mounted on the upper side of the beam while strain gauges 39 and 49 are mounted on the lower side of the beam, and the longi tudinal axes of the strain gauges are parallel to the longitudinal axis of the beam 34. Preferably, the strain gauges are mounted near the attached end of the beam 34 so that the strain gauges, their leads &1 and a connector 42 may all be conveniently protected by a covering 43 (removed in FIG. 2). This tension sensing assembly is highly responsive because of its inherent sensitivity and low inertia.

Referring particularly to FIG. 3, strain gauges 37 to it) are electrically connected into a bridge arrangement wherein one terminal of an oscillator 44 generating a frequency of 2400 c.p.s. is connected between strain gauges 37 and 39 and the other terminal of the oscillator 44- is connected between strain gauges 4t and 38. A resistor 45 with an adjustable tap 46 to ground is connected between strain gauges 37 and 40 and an amplifier 47 is connected to a terminal between strain gauges 38 and 39.

A thyratron circuit 49 is provided to supply the current to coils 27. The thyratron circuit 49 has an alternating plate supply and the firing time is controlled to supply a normal amount of current to coils 27 sufiicient to generate the rotation-retarding force on the disk 29. The firing time may be controlled either by a direct grid Voltage or by phase shifting of an alternating grid voltage, in the well known manner explained in Gray, Applied Electronics (New York, Wiley, 1954), pp. 365-382. Variations in the tension from this normal state are sensed in the bridge circuit. The output of the bridge circuit is amplified in an amplifier 47 and rectified in a rectifier 43. The output of the rectifier 4-8 is used to control the thyratron circuit '49 to vary its firing time to compensate for the change in tension, bringing the tension back to normal.

The apparatus described above is capable of accurate and highly responsive tension control. In one test with the motor running at 12,000 rpm. the tension between the spool 13 and the disk 29- was maintained within 5 percent of grams while 40,000 turns of 44 gauge wire were wound on the spool 13.

It is to be understood that the above described embodiment of the invention is merely illustrative and that numerous modifications may be made within the spirit and scope of the invention.

What is claimed is:

1. Apparatus for tensioning a strand advancing between a strand supply means and a strand receiving means, comprising a rotatable conductive disk having a periphery around which the strand is wrapped, said disk engaging the strand between said strand supply means and said strand receiving means, an electromagnet having at least one pole piece adjacent each side of said disk near the periphery of the disk, and means for supplying electrical energy to said electromagnet to induce a rotation-retarding eddycurrent in said disk, a flexible cantilevered beam, a pulley mounted on the free end of the beam, the strand passing over a portion of said pulley so that said beam is deflected dependent upon strand tension, electrical resistance type strain gauge means fixed to at least one surface of said beam for measuring the strain caused by the deflection of the beam the electrical resistance of said strain gauge means varying with changes in the deflection of the cantilevered beam, and means for changing the output of said electrical energy supply means in response to resistance changes of said strain gauge means to stabilize the strand tension at a predetermined value.

2. Apparatus for tensioning a filamentary strand advancing between a stationary supply reel and a rotatable strand take-up spool comprising a rotatable, low inertia, aluminum wheel having a hub, a plurality of spokes, and a rim with a peripheral groove, the strand being looped approximately once around said rim within the groove for engaging the strand between said supply reel and said take-up spool, a pair of back tensioning rollers engaging the strand between said wheel and said supply reel to provide a firm engagement of said wheel by the strand, an electromagnet having two pole pieces the ends of which are separated a sufficient distance to permit the rotation of the rim portion of said wheel therebetween, a controllable electrical energy source connected to said electromagnet to induce a rotation-retarding eddy-current in the rim portion of said wheel, a flexible cantilevered beam, at light weight, free wheeling pulley mounted on the free end of the beam, the strand passing over a portion of the pulley so that the beam is deflected dependent upon strand tension, at Wheatstone bridge having an input and an output circuit, first and second strain responsive transducers connected in separate and opposite branches of the bridge and fixed to one side of the beam, third and fourth strain responsive transducers connected in separate and opposite branches of the bridge and fixed to the other side of the beam, the transducers being mounted immediately adjacent to' the fixed end of the beam and having electrical resistance which vary with the strains induced in the deflected beam a source of alternating current connected to the input circuit of the bridge, the output of the bridge being determined by the magnitude of the beam deflection, and means responsive to the output of said bridge for controlling said electrical energy source so as to tend to maintain a desired predetermined strand tension.

3. Apparatus in accordance with claim 1 wherein the strain gauge means comprises at least two resistance type strain gauges fixed to opposite faces of the cantilevered beam immediately adjacent to the supported end thereof so that when the beam is deflected the effective resistance of one strain gauge increases while the effective resistance of the other of the strain gauges decreases, and the means for changing the output of the supply means comrises a Wheatstone bridge including the resistances of the two strain gauges connected respectively into two adjacent bridge arms, and means responsive to the output of the bridge for controlling the output of the supply means.

References Cited in the file of this patent UNITED STATES PATENTS 2,586,087 Heffelfinger Feb. 19, 1952 2,601,961 Stephenson July 1, 1952 2,624,527 Von Kohorn Jan. 6, 1953 2,688 789 Duryee Sept. 14, 1954 

1. APPARATUS FOR TENSIONING A STRAND ADVANCING BETWEEN A STRAND SUPPLY MEANS AND A STRAND RECEIVING MEANS, COMPRISING A ROTATABLE CONDUCTIVE DISK HAVING A PERIPHERY AROUND WHICH THE STRAND IS WRAPPED, SAID DISK ENGAGING THE STRAND BETWEEN SAID STRAND SUPPLY MEANS AND SAID STRAND RECEIVING MEANS, AN ELECTROMAGNET HAVING AT LEAST ONE POLE PIECE ADJACENT EACH SIDE OF SAID DISK NEAR THE PERIPHERY OF THE DISK, AND MEANS FOR SUPPLYING ELECTRICAL ENERGY TO SAID ELECTROMAGNET TO INDUCE A ROTATION-RETARDING EDDY-CURRENT IN SAID DISK, A FLEXIBLE CANTILEVERED BEAM, A PULLEY MOUNTED ON THE FREE END OF THE BEAM, THE STRAND PASSING OVER A PORTION OF SAID PULLEY SO THAT SAID BEAM IS DEFLECTED DEPENDENT UPON STRAND TENSION, ELECTRICAL RESISTANCE TYPE STRAIN GAUGE MEANS FIXED TO AT LEAST ONE SURFACE OF SAID BEAM FOR MEASURING THE STRAIN CAUSED BY THE DEFLECTION OF THE BEAM THE ELECTRICAL RESISTANCE OF SAID STRAIN GAUGE MEANS VARYING WITH CHANGES IN THE DEFLECTION OF THE CANTILEVERED BEAM, AND MEANS FOR CHANGING THE OUTPUT OF SAID ELECTRICAL ENERGY SUPPLY MEANS IN RESPONSE TO RESISTANCE CHANGES OF SAID STRAIN GAUGE MEANS TO STABILIZE THE STRAND TENSION AT A PREDETERMINED VALUE. 